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Aims of the project DINAMIS

• make a general dynamical description of how molecules form objects
such as micelles in water environment

• advance the understanding of dynamical processes in micro-segregated systems
by using computer simulations and theoretical methods

• relate the results with the available experiments

• develop the dynamical density functional theory and apply
the theory to model and realistic systems

OUR TEAM


Boss

Bernarda Lovrinčević, assistant professor

Group leader
Boss

Ivo Jukić

PhD student
Boss

Martina Požar, assistant professor

Scientific associate

Dynamics in micro-segregated systems

About the project

Better understanding of structure and dynamics in mixtures, especially aqueous mixtures, will impact on some important scientific topics, such as green chemistry and biophysics. The focus of green chemistry is to construct commercial products and new drugs, and to preserve environment at the same time. The central part of this project deals with alcohols, alkanes, water, ethers and their mixtures. Alcohols are in general used as solvents, as fuels, in food productions and in medicine. Ethers are used as solvents and in industrial purposes.

In particular, 2-Isobutoxyethanol is used in oil industry as a non-toxic, non-expensive surfactant (Rodgers et al., 2015). Water is the most important liquid on Earth and its role in biological processes, such as protein folding, enzymatic reactions and object formation is not yet fully understood. Electrostatic interactions play a key role in the micro-segregation of molecules and its dynamics in binary mixtures aqueous mixtures. There is interplay between the hydrophobic and the hydrophilic interactions that govern the process dynamics.
Depending on the solute chemical composition, water reorganises itself in such a way that the free energy of the system reaches a minimum, which results in the formation of domains or even micelles. The dynamics of these domains is still not completely understood, and neither is the difference between concentration fluctuations and the emerging objects in these systems. Clearly, these two are separate phenomena, the former being present also in ideal mixtures, while the latter relates only to particular types of systems, such as the hydrogen-bonded mixtures or ionic liquid mixtures. This was confirmed in previous studies by the members of this group, both in model (Kežić-Lovrinčević, Dartois and Perera, 2015) and realistic systems (Kežić and Perera, 2012a;Kežić and Perera, 2012b)

What is missing from all these studies is the description of fluctuations and object formation in terms of different time scales. This taken into account, the best systems to study these phenomena are those where objects have a well-defined shape so one can clearly differentiate between an object and concentration fluctuation. However, the information about the dynamics of these newly formed structures are rather scarce, especially in the field of molecular dynamics simulations, where the results strongly depend on the computational resources.

Lights

Snapshot of ethanol-hexane mixture for 20% ethanol. Only ethanol oxygen (red) and hydrogen (white) atoms are shown to visualise better the spatial organisation of ethanol molecules. M. Požar, B. Lovrinčević, L. Zoranić, T. Primorac, F. Sokolić, A. Perera, 2016.

We aim at understanding the lifetime of newly formed objects and their kinetics, which is a problem that lies at the heart of biophysics and material science. Molecular dynamics simulations and theoretical approaches ensure solutions where experimental evidence becomes questionable.

Transport properties, such as diffusion constants, viscosity and thermal conductivity, are of particular interest, since they affect most of the chemical processes. Autocorrelation functions, such as the velocity-velocity autocorrelation function give useful description about the dynamics in the liquid system. Simulations have shown to be quite useful in the calculation of the transport properties and autocorrelation functions in the recent studies of both aqueous and non-aqueous mixtures. Another great advantage of simulations is that they can enable the calculation of both static and dynamic properties of the system, giving at the same time deep insight on the microscopic level. This is particularly valuable in the study of biologically relevant systems and water mediated processes, such as the hydrophobic effect.

Lights

Vibrational power spectra of ethanol O and H atoms in ethanol-water (left panel) and ethanol-hexane (right panel). Color convention: xE = 0.1 (magenta), xE = 0.2 (black), xE = 0.3 (dark green), xE = 0.4 (purple), xE = 0.5 (red), xE = 0.6 (cyan), xE = 0.7 (orange) and xE = 0.8 (green). O and H labels are indicated in the panels. From: I. Jukić, M. Požar and B. Lovrinčević, Phys. Chem. Chem. Phys. 22, 23856-23868 (2020)

In the past, there have been many studies focusing on the simplest systems governed by the hydrophobic effect - aqueous mixtures. Both simulation and experimental studies have confirmed micro-segregation of the constituent molecules and the existence of water domains. But, the time evolution of these domains is not fully understood. Application of dynamic theory to realistic liquids has been mostly limited to simple liquids, typically Lennard-Jones liquids, but also weakly polar liquids.

In this perspective, it is important to understand that the extension of these approaches to associating liquids does not consist simply of accounting for yet another type of interaction - the associating interactions, but it would rather consist of taking into account the new physical phenomena that result from this interaction, namely micro-segregation. In order to better appreciate this point, it is noteworthy to recall that the hydrogen bonding of water under cooling undergoes a dramatic change in the local clustering. Obviously, this exceptional plasticity of water needs to be either described as a consequence of the type of interactions (hydrogen bonding), or to be directly incorporated into the theory.
It is this dual aspect which motivates our desire for a new approach of dynamics.

Results

Contact

University of Split

Faculty of Science

Ruđera Boškovića 33

21 000 Split, HR

+38521 619245

  bernarda@pmfst.hr